Such a method is known from HSIEH, J. et al., “A novel reconstruction algorithm to extend the CT scan field-of-view”, MED. PHYS. 31 (9), September 2004, pages 2385 to 2391. With the known method truncation artifacts can be suppressed but then appear when the object to be examined extends into regions outside what is known as the measuring field region. The resulting projection images are referred to as cut off or truncated. Truncated projection images produce artifacts when the sectional images are reconstructed. In particular the image values close to the edges in the sectional images are generally too high and in a central region they are too low. The sectional images affected by truncation artifacts are therefore of only limited value for diagnosis purposes.
With the known method an equivalent body is constructed in the peripheral region of a projection image, when there is attenuation there, to produce the same attenuation as the object to be examined in the peripheral region. The equivalent body is then projected onto the region outside the projection image using parallel beam geometry. This means that the projection image is continued in a region outside the projection image.
The projection of the equivalent body using parallel beam geometry onto the region outside the projection image requires the fan beam data recorded using fan beam geometry to be converted to parallel beam data. Conversion of the fan beam data to parallel beam data is also referred to as rebinning. What is known as rebinning is computation-intensive and cannot be used in all instances. With computed tomography recordings with C-arm systems in particular the waiting and computation times required for rebinning are not available due to the reconstruction times, which are in any case very long.